The present invention relates to fuel oil compositions, processes for their preparation, and their use in compression-ignition engines.
As stated in WO 9533805 (Exxon) environmental concerns have led to a need for fuels with reduced sulphur content, especially diesel fuel and kerosene. However, the refining processes that produce fuels with low sulphur contents also result in a product of lower viscosity and a lower content of other components in the fuel that contribute to its lubricity, for example, polycyclic aromatics and polar compounds. Furthermore, sulphur-containing compounds in general are regarded as providing anti-wear properties and a result of the reduction in their proportions, together with the reduction in proportions of other components providing lubricity, has been an increase in reported failures of fuel pumps in diesel engines using low-sulphur fuels, the failure being caused by wear in, for example, cam plates, rollers, spindles and drive shafts.
This problem may be expected to become worse in the future because, in order to meet stricter requirements on exhaust emissions generally, high pressure fuel pumps, for example rotary and unit injector systems, are being introduced, these being expected to have more stringent lubricity requirements than present equipment, at the same time as lower sulphur levels in fuels become more widely required.
At present, a typical sulphur content in a diesel fuel is about 0.25% by weight (2500 ppmw). In Europe maximum sulphur levels are being reduced to 0.20% (2000 ppmw), and are expected to be reduced to 0.05% (500 ppmw); in Sweden grades of fuel with levels below 0.005% (50 ppmw) (Class 2) and 0.001% (10 ppmw) (Class 1) are already being introduced. Fuel oil compositions with a sulphur level below 0.20% by weight (2000 ppmw) may be referred to as a low-sulphur fuels.
WO 95 33805 (Exxon) describes the use of cold flow improvers to enhance lubricity of low-sulphur fuels.
WO 94 17160 (Exxon) describes the use of certain esters of a carboxyclic acid and an alcohol wherein the acid has from 2 to 50 carbon atoms and the alcohol has one or more carbon atoms, particularly glycerol monooleate and di-isodecyl adipate, as additives for fuel oils for wear reduction in the injection system of a compression-ignition engine.
U.S. Pat. No. 5,484,462 (Texaco) mentions dimerized linoleic acid as a commercially available lubricity agent for low sulphur diesel fuel (Col. 1, line 38), and itself provides aminoalkylmorpholines as fuel lubricity improvers.
U.S. Pat. No. 5,490,864 (Texaco) describes certain dithiophosphoric diester-dialcohols as anti-wear lubricity additives for low-sulphur diesel fuels.
It has now surprisingly been found that certain alkyl and alkoxy aromatic compounds having at least one carboxyl group attached to their aromatic nuclei can confer anti-wear lubricity effects when incorporated in fuel oil.
According to the present invention therefore there is provided a fuel oil composition comprising a major amount of a fuel oil and a minor amount of an additive comprising at least one fuel oil soluble alkyl or alkoxy aromatic compound wherein at least one group independently selected from alkyl and alkoxy groups of 1 to 30 carbon atoms is attached to an aromatic nucleus and at least one carboxyl group and optionally one or two hydroxyl groups are attached to the aromatic nucleus.
The fuel oil may be derived from petroleum or from vegetal sources or a mixture thereof. It may conveniently be a middle distillate fuel oil having a boiling range in the range 100xc2x0 C. to 500xc2x0 C., e.g. 150xc2x0 C. to 400xc2x0 C. Petroleum-derived fuel oils may comprise atmospheric distillate or vacuum distillate, or cracked gas oil or a blend in any proportion of straight run and thermally and/or catalytically cracked distillates. Fuel oils include kerosine, jet fuels, diesel fuels, heating oils and heavy fuel oils. Preferably the fuel oil is a diesel oil, and preferred fuel oil compositions of the invention are thus diesel fuel compositions. Diesel fuels typically have initial distillation temperature of about 160xc2x0 C. and final distillation temperature of 290-360xc2x0 C., depending on fuel grade and use.
A fuel oil, e.g. diesel oil, itself may be an additised (additive-containing) oil or an unadditised (additive-free) oil. If the fuel oil, e.g. diesel oil, is an additised oil, it will contain minor amounts of one or more additives, e.g. one or more additives selected from anti-static agents, pipeline drag reducers, flow improvers (e.g. ethylene/vinyl acetate copolymers or acrylate/maleic anhydride copolymers) and wax anti-settling agents (e.g. those commercially available under the Trade Marks xe2x80x9cPARAFLOWxe2x80x9d (e.g. xe2x80x9cPARAFLOWxe2x80x9d 450; ex Paramins), xe2x80x9cOCTELxe2x80x9d (e.g. xe2x80x9cOCTELxe2x80x9d W 5000; ex Octel) and xe2x80x9cDODIFLOWxe2x80x9d (e.g. xe2x80x9cDODIFLOWxe2x80x9d v 3958; ex Hoechst).
Preferably the fuel oil is a middle distillate oil, e.g. a diesel oil, having a sulphur content of at most 0.2% by weight (2000 ppmw) (xe2x80x9cppmwxe2x80x9d is parts per million by weight), more preferably at most 0.05% by weight (500 ppmw). Advantageous compositions of the invention are also attained when the sulphur content of the fuel oil is below 0.005% by weight (50 ppmw) or even below 0.001% by weight (10 ppmw).
Although the aromatic nucleus of the alkyl or alkoxy aromatic compound may be monocyclic, bicyclic or polycyclic, e.g. a benzene ring or a naphthalene ring system, the aromatic nucleus is preferably a benzene ring.
Preferred alkyl and alkoxy aromatic compounds are those in which whenever there are less than three groups selected from alkyl and alkoxy groups attached to the aromatic nucleus, there is at least one group selected from alkyl and alkoxy groups of 2 to 30 carbon atoms attached to said nucleus.
In one preferred aspect of the present invention, the at least one alkyl or alkoxy aromatic compound is an alkyl aromatic compound wherein at least one alkyl group of 6 to 30 carbon atoms is attached to the aromatic nucleus.
More preferably, the alkyl aromatic compound is an alkyl benzoic acid or an alkyl salicylic acid containing one or two alkyl groups of 6 to 30 carbon atoms.
The or each alkyl group in the alkyl aromatic compound is preferably a C8-22 alkyl group, most preferably a C8-18 alkyl group.
The alkyl or alkoxy aromatic compounds incorporated in fuel oil compositions of the present invention are either known compounds or can be prepared by methods analogous to methods used for preparing known compounds, as will readily be appreciated by those skilled in the art.
Preferred alkyl salicylic acids may be very readily be prepared by the methods described in UK Patent 1,146,925, incorporated herein by reference. (In that patent, the alkyl salicylic acids are intermediates in the preparation of polyvalent metal salts used as dispersants in lubricant compositions).
The additive comprising the at least one alkyl or alkoxy aromatic compound is preferably present in an amount in the range 50 to 500 ppmw, more preferably 50 to 250 ppmw, most preferably 150 to 250 ppmw, based on the total weight of the fuel composition.
Fuel oil compositions in accordance with the invention may be prepared by a process for their preparation which comprises admixing the additive or an additive concentrate containing the additive-with the fuel oil.
Additive concentrates suitable for incorporating in the fuel oil compositions (preferably diesel fuel compositions) will contain the additive comprising the at least one alkyl aromatic compound and a fuel-compatible diluent, which may be a carrier oil (e.g. a mineral oil), a polyether, which may be capped or uncapped, a non-polar solvent such as toluene, xylene, white spirits and those sold by member companies of the Royal Dutch/Shell Group under the Trade Mark xe2x80x9cSHELLSOLxe2x80x9d, and/or a polar solvent such as esters and, in particular, alcohols, e.g. hexanol, 2-ethylhexanol, decanol, isotridecanol and alcohol mixtures such as those sold by member companies of the Royal Dutch/Shell Group under the Trade Mark xe2x80x9cLINEVOLxe2x80x9d, especially xe2x80x9cLINEVOLxe2x80x9d 79 alcohol which is a mixture of C7-9 primary alcohols, or the C12-14 alcohol mixture commercially available from Sidobre Sinnova, France under the Trade Mark xe2x80x9cSIPOLxe2x80x9d.
Additive concentrates and fuel oil compositions prepared therefrom may further contain additional additives such as ashless detergents or dispersants, e.g. linear or branched hydrocarbyl amines, for example alkylamines, hydrocarbyl-substituted succinimides, such as those described in EP-A-147 240, preferably the reaction product of a polyisobutylene succinic acid or anhydride with tetraethylene pentamine wherein the polyisobutylene substituent has a number average molecular weight (Mn) in the range 500 to 1200, and/or an alkoxy acetic acid derivative as described in European Application No. 96302953.3 (Applicant""s reference TS 7030 EPC); dehazers, e.g. alkoxylated phenol formaldehyde polymers such as those commercially available as xe2x80x9cNALCOxe2x80x9d (Trade Mark) EC5462A (formerly 7D07) (ex Nalco), and xe2x80x9cTOLADxe2x80x9d (Trade Mark) 2683 (ex Petrolite); anti-foaming agents (e.g. the polyether-modified polysiloxanes commercially available as xe2x80x9cTEGOPRENxe2x80x9d (Trade Mark) 5851, Q 25907 (ex Dow. Coming) orxe2x80x9cRHODORSILxe2x80x9d (ex Rhone Poulenc)); ignition improvers (e.g. 2-ethylhexyl nitrate, cydohexyl nitrate, di-tertiarybutyl peroxide and those disclosed in U.S. Pat. No. 4,208,190, incorporated herein by reference, at Column 2, line 27 to Column 3, line 21); anti-rust agents (e.g. that commercially sold by Rhein Chemie, Mannheim, Germany as xe2x80x9cRC 4801xe2x80x9d, or polyhydric alcohol esters of a succinic acid-derivative, the succinic acid derivative having on at least one of its alpha-carbon atoms an unsubstituted or substituted aliphatic hydrocarbon group containing from 20 to 500 carbon atoms, e.g. the pentaerythritol diester of polyisobutylene-substituted succinic acid), reodorants, anti-wear additives; anti-oxidants (e.g. phenolics such as 2,6-di-tert-butylphenol, or phenylenediamines such as N,Nxe2x80x2-di-sec-butyl-p-phenylenediamine); and metal deactivators.
Unless otherwise stated, the (active matter) concentration of each additional additive in the diesel fuel is preferably up to 1 percent by weight, more preferably in the range from 5 to 1000 ppmw (parts per million by weight of the diesel fuel). The (active matter) concentration of the detergent or dispersant in the diesel fuel is preferably 30 to 1000 ppmw, more preferably 50 to 600 ppmw, advantageously 75 to 300 ppmw e.g. 95 to 150 ppmw.
The (active matter) concentration of the dehazer in the diesel fuel is preferably in the range from 1 to 20 ppmw, more preferably from 1 to 15 ppmw, still more preferably from 1 to 10 ppmw and advantageously from 1 to 5 ppmw. The (active matter) concentrations of other additives (with the exception of the ignition improver are each preferably in the range from 0 to 20 ppmw, more preferably from 0 to 10 ppmw. The (active matter) concentration of the ignition improver in the diesel fuel is preferably in the range from 0 to 600 ppmw and more preferably from 0 to 500 ppmw. If an ignition improver is incorporated into the diesel fuel, it may conveniently be used in an amount of 300 to 500 ppmw.
The invention further provides the use of a fuel composition as defined above as fuel in a compression-ignition engine for controlling wear rate in the fuel injection system of the engine, especially in fuel injection pumps and/or fuel injectors.
This latter aspect of the invention may also be expressed as a method of operating a compression-ignition engine which comprises providing a fuel composition as defined above as the fuel in the engine thereby to control wear rate in the fuel injection system of the engine, especially the fuel injection pump and/or fuel injectors.
The invention will be further understood from the following illustrative examples which are included for illustrative purposes only and are in no way intended to limit the present invention.